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This paper presents the results of a sedimentological study of three alluvial fans in the town of Ejido in the Municipality of Campo Elias in Merida State. The alluvial fans in the Montalban - La Ceibita Basin are linked to distinct events that occurred in the area. The fan profiles are related to the supply of high volumes of sediment caused by unstable geological settings, unfavorable geomorphological processes and exceptional hydrometereological conditions. Grain size and mineral composition differences observed in samples and profiles reveal lithofacies and paleocurrent changes that vary from one fan to another.
Therefore, the three alluvial fans represent different sedimentation mechanisms linked to debris flow (the La Vega fan in Ejido). According to sedimentological studies, the La Vega fan is related to the flooding of the Montalban River, which is a product of a sporadic natural phenomenon (rainfall) that increases both erosion and sediment load, depending on the duration and intensity of a given precipitation event. In the case of the La Vega fan of Ejido, sedimentological analysis suggests that the destructive debris flows of 1947 resulted from the failure of a natural dam in the headwaters of the basin. Cosmogenic 35 Cl exposure dating of rock avalanche deposits in the area of El Minual indicate that at least three similar mass flows have occurred in the past 1,000 to 2,000 years.
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